In the related art, an on/off valve disposed in a piping system that handles liquid, such as a chemical solution, is provided with a separate suck-back only valve alongside thereof to prevent liquid dripping (fluid drops) from occurring during a fully closing operation. Such a suck-back only valve operates in synchronization with the closing operation of the on/off valve and can prevent liquid dripping by sucking the liquid at an outlet side to a suck back chamber side by operating a diaphragm in a direction in which the volume of the suck back chamber is increased (for example, refer to Patent Citation 1)
Moreover, because the on/off valve and the suck back valve described above are separate from each other, an integral-type suck back valve with a structure in which both valves are integrated has been proposed by the applicant with the aim of reducing the installation space of the entire apparatus and solving the problem of synchronizing the actuator etc.
On the other hand, a protective on/off valve is sometimes disposed at the upstream side of the integral-type suck back valve as a protective measure in the event that the integral-type suck back valve malfunctions. For the suck back valve system configured having both the integral-type suck back valve and the protective on/off valve in this manner, it is desirable to operate the protective on/off valve provided as a measure against the malfunction of the integral-type suck back valve at a position as close as possible to the integral-type suck back valve with the minimum time lag to minimize the fluid outflow in the event that the integral-type suck back valve is not closed (not operated).
Patent Citation 1: Japanese Unexamined Patent Application, Publication No. 2002-316085